SHRIMP U–Pb ages of ultrahigh‐pressure and retrograde metamorphism of gneisses, south‐western Sulu terrane, eastern China

Journal of Metamorphic Geology - Tập 22 Số 4 - Trang 315-326 - 2004
Fulai Liu1, Zhiqin Xu1, J. G. Liou2, Biao Song1
1Institute of Geology, Chinese Academy of Geological Sciences,Beijing, 100037, China ([email protected])
2Department of Geological and Environmental Sciences, Stanford University, Stanford, CA 94305 USA

Tóm tắt

AbstractLaser Raman spectroscopy and cathodoluminescence (CL) images reveal that most zircon separated from paragneiss and orthogneiss in drillhole CCSD‐PP2 at Donghai, south‐western Sulu terrane, retain low‐P mineral‐bearing inherited cores, ultrahigh‐pressure (UHP) mineral‐bearing mantles and low‐P mineral‐bearing (e.g. quartz) rims. SHRIMP U–Pb analyses of these zoned zircon identify three discrete and meaningful age groups: Proterozoic protolith ages (> 680 Ma) are recorded in the inherited cores, the UHP metamorphic event in the coesite‐bearing mantles occurred at 231 ± 4 Ma, and the late amphibolite facies retrogressive overprint in the quartz‐bearing rims was at 211 ± 4 Ma. Thus, Neoproterozoic supracrustal protoliths of the Sulu UHP rocks were subducted to mantle depths in the Middle Triassic, and exhumed to mid‐crustal levels in the Late Triassic. The exhumation rate deduced from the SHRIMP data and metamorphic P–T conditions is 5.0 km Ma−1. Exhumation of the Sulu UHP terrane may have resulted from buoyancy forces after slab break‐off at mantle depths.

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Journal of Metamorphic Geology

Tập 22 Số 4

315-326

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